Synchronous cut-off device



April 19, 1966 T. o. WILLIAMS SYNCHRONOUS CUTOFF DEVICE Filed July 16, 1962 I NVENTOR.

mmjomkzou T 9 5% 5: (W QAV m di THOMAS O. WILLIAMS ATTORNEY ,tinuous weld tube mills.

of a differential detector.

United States Patent 3,246,380 SYN CHRONOUS CUT-OFF DEVICE Thomas ,0. Williams, Painesville, Ohio, assignor to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Filed July 16, 1962, Ser. No. 210,621 '20 Claims. ((11. 29-33) The present invention relates generally to the manufacture of tubes and other shapes which are produced in a continuousmanner and are then cut into preselected lengths and relates more particularly to an apparatus for cutting such lengths.

The present invention has particular utility in con- Here tubing is formed from a longv strip of steel by continuously feeding the strip into a forming section. In this forming section the strip is formed into a tube of cylindrical or other shape and then welded along its longitudinalseam. This tube manufacturing operation is continuous making it necessary for the cutoff device to be moving at the speed of the finished tube each-time a length is cut from the tube.

Over the years many inovations have increased the operational-speed of the tube mill to apoint where at least prior to this invention the maximum speed of the mill has beenlimited primarily by the operation of the cutoff device. The problem which causes the cut-off deviceto limit the speed of the tube mill is that of coordinating the operation of the cut-off device to the travel of the moving tubing so as to achieve uniformity in the cut lengths of tube. It the operation of the cut-off device is not accurately controlled so that it is in step at all times with the tube travel, the cut pieces will vary in length.

In1many of the present day mills the operation of the cut-off device is-timed from the rotation of the sizing rolls. After a given number of revolutions of the sizing rolls the tube is severed. Unfortunately, this type of control system has not produced cut tubes of a uniform length. It has been found that although the rolls may rotate at a uniform speed, the tube exit speed often varies. This variation in the tube exit speed is believed to be due to variations in both roll slippage and in tube elongation.

The present invention overcomes these problems of the prior art by relating the operation of the cut-off device to the actual tube travel rather than to sizing roll rotation. To accomplish this a control system is provided which maintains a coordinated relationship between cut-off travel and tube travel at all times. The control system auto- .matically correctsfor a change in the rate of one of these speeds of travel, preferably tube exit speed, so that every cut piece of tube is of a given uniform length.

The preferred control system includes a tachometer generatorto detect the speed of the operation of the cutoff device. The input shaft of the tachometer generator is driven by the drive mechanism for the cut-off device. The electrical output of the tachometer generator is fed to a synchronous motor. The output shaft of the synchr-onous motor is connected to one of two input shafts The other input shaft of the differential detector ir rotated at a speed which is proportional to the actual tube travel. The output of the differential detector is connected to a controller for the drive mechanism to adjust the operating speed of the cut-off device to maintain it in exact step with the tube travel.

Selected changes in tube lengths are obtained by a selsyn which is electronically interposed between the tachometer generator and the synchronous motor. Depending upon the direction its shaft is rotated the vernier selsyn either adds to or subtracts fromthe frequency of the tachometer generator voltage output. The output shaft of the synchronous motor accordingly rotates either faster or slower than it would if the vernier selsyn were not provided. The differential detector senses the increased speed of the synchronous motor and adjusts the speed of the cut-off device to maintain the latter in exact step with the tube travel. The frequency of cut per unit of tube travel thus changes providing a different length of cut tube. The exact length of the cut pieces of tube is preselected and changed by adjusting the input shaft speed of the vernier selsyn.

The advantage produced by the automatic synchronous control system of the present invention is that cut pieces of tube will be of a uniform length regardless of any change in tube travel while the tube is being produced. The adjustments in the operating speed of the cut-off device are made automatically while the mill is running so that it is not necessary to stop the mill to make such changes. The preselected length is quickly set by the vernier selsyn and may be changed at any time, even while the mill is running.

Accordingly, one feature of the present invention is the provision of a new and improved control system for use in continuous mill operations wherein the operation of the cut-off device is accurately related to actual tube travel to provide cut pieces of tube of a uniform preselected length.

Another feature of the present invention is to provide a control system for use in a continuous mill operation wherein the operation of the cut-off device is accurately related to tube travel and is not affected by variations in roll slippage and the tube elongation such that finished tubes of a uniform preselected length are produced.

A further feature of the present invention is to provide a control system for use in continuous mill operations wherein the operation of the cut-off device is accurately related to the tube travel by a differential synchronous control system which compares the operating speed of the cut-off device to the actual tube travel and automatically adjusts one to be in step with the other.

Yet another feature of the present invention is to provide a control system which synchronizes the operation of the cut-off device to the tube travel by comparing the speed of operation of the cut-off device to the tube travel and automatically maintains one in step with the other, and wherein the length of the pipe may be set by introducing an artificial differential between the operating speed of the cut-olf device and the tube travel.

The present invention will be better understood by those skilled in the art by the following description of the drawing, in which:

FIGURE 1 is a schematic drawing of a continuous- Weld tube mill utilizing the control apparatus of the present invention; and,

FIGURE 2 is a side view of a part of the system of FIGURE 1.

The drawing is a schematic showing of a typical pipeforming mill utilizing the preferred form of the synchronous cut-oif The pipe forming mill includes a forming section 11, a welding section 12, a sizing section 13 and a cut-off press 14.

A strip of steel, or skelp, 15 is introduced continuously into the forming section 11 Where it is bent longitudinally to form an elongated tube form 16 usually of cylindrical configuration. The form 16 passes from the forming section into the welding section 12 wherethe butted longitudinal edges are welded to form a seamed tube 17. The tube 17 then passes through the sizing section 13 where it is rolled to its final dimensions. Finally the cut-oif press 14 cuts the continuously moving tube into specified lengths.

control The cut-off press 14 includes a shear member 18 and a die member 19. As shown in the drawing, the die member 19 includes two die member halves 19, 19" which are permanently fastened together and are separated by a distance sufficient to allow the shear member 18 to operate between them. The shear and die members 18, 19 are mobilely carried by the cut-off press 14 and reciprocate in a path parallel to the axis of the moving tube 17. An oscillator drive mechanism is provided to reciprocate the shear and die members. The oscillator drive mechanism includes an oscillator rod 21 to move the shear and die members back and forth, a rotating bull gear 22, and a pitman arm 23 to translate the rotary motion of the bull gear 22 to the substantially reciprocating motion of the oscillator rod 21. A crankpin 25 projects from the bull gear 22 and is slidably disposed in a slot 26 in the pitman arm 23. As the bull gear rotates, the coaction between the crankpin 25 and the slot 26 causes the upper end of the pitman arm to oscillate about its lower, pivotally secured end. The oscillator rod 21 is connected between the oscillating upper end of the pitman arm and the shear and die members 18, 19.

When the crankpin 25 is at the extreme left position of its orbit (as viewed when facing the drawing) the shear and die members are in a position nearest the sizing section. At this time the shear and die members commence to travel in the same direction as the tube for a cutting operation. As the bull gear rotates in the counterclockwise direction indicated by the arrow 28 the shear and die members are accelerated in the direction of the moving tube 17. When the crankpin 25 is at the bottom of its orbit, the shear and die members have the forward velocity of the tube 17. At this instant a cam portion 30 on the die member 19 strikes a limit switch 31 to signal a control mechanism (not shown) in the cut-off press to cause the shear member 18 to descend and cut the tube 17,

The drawing shows the crank pin 25 approaching the bottom of its orbit. As the crankpin 25 runs through the upward and extreme right portion of its orbit the shear and die members 18, 1-9 are decelerated to a stop and then accelerated on their return movement. Finally, the shear and die members 18, 19 are decelerated to the position where the crankpin is again at its extreme left position. The oscillating drive mechanism is operating continuously and in synchronism with the moving tube so that each time the crankpin 25 reaches the bottom of its orbit a length of tube is cut.

An oscillator drive motor 34 is provided to motivate the oscillator drive mechanism. An output shaft of the drive motor 34 is operatively connected to a drive input shaft 35 of the oscillator drive mechanism by a suitable chain drive 36. The input shaft 35 turns a set of bevel gears 37. The bevel gears 37 turn a spur gear train 38 to cause the bull gear to rotate.

The drive motor armature circuit 39 is connected to a suitable DC. voltage supply E. The magnitude of the electrical energy supplied to the armature circuit 39 is controlled by the oscillator motor speed controller 40. The field winding circuit 41 of the oscillator drive motor is connected to a suitable DC. voltage supply E A field rheostat 43 is provided in the field winding circuit 41 to vary the voltage supplied to the motor field winding.

A synchronous control system is provided to maintain the input shaft speed of the oscillator drive mechanism in exact step with the rate of tube travel. The synchronous control system includes three-phase tachometer generator 45 driven at the oscillator mechanism input shaft speed by the chain drive 36. The voltage output of the tachometer generator 45 is fed to a synchronous motor 46 by conductors 47, 43. The rotation of the armature of the synchronous motor 46 will exactly follow that of the tachometer generator 45 in the manner of the usual self-synchronous system. An example of a typical selfsynchronous system is found on page 527 of Electric Machinery by Fitzgerald and Kingsley, published by McGraw-Hill Book Company, Inc., New York, 1952, Library of Congress catalogue card No. 51-12939.

A vernier, or differential, selsyn 51 is provided and is electrically interposed between the synchronous motor 46 and the tachometer generator 45. Preferably, the stator windings of the differential selsyn 51 are connected tothe output of the tachometer generator 45. Its rotor windings are connected to the input of the synchronous motor 46. A differential selsyn drive motor 53 is provided and is operatively connected to the input shaft of the differential selsyn 51. Rotation of the input shaft of the differential selsyn in one direction adds to, and rotation in an opposite direction subtracts from, the frequency of the tachometer generator voltage output so as to cause the output shaft 54 of the synchronous motor 46 to run faster, or slower, respectively. The complete function of the differential selsyn will be explained more fully below.

The output shaft 54 of the synchronous motor is connected to drive a bevel gear 55 in an error detector differential system 59. A tube travel measuring device is provided and includes a wheel 56 driven by the moving tube. The wheel 56 is connected through a suitable shaft and coupled to drive a bevel gear 57 of the differential system 59. The drive wheel 56 is positioned against the tube 17 after it leaves the sizing section 13 so that the retational speed of the bevel gear 57 accurately corresponds to the actual lineal travel of the moving tube. V

The function of the error detector differential system 59 is to compare the rotational speed of the synchronous motor 46 to that of the tube driven wheel 56 by means of bevel gears 55, 57. A pair of planet gears 58, 60 are operatively associated with the bevel gears 55, 57 and will rotate together about the axis of the bevel gears 55, 57 if there is any differential between the rotational speed of the synchronous motor 46 and the pipe driven wheel 56.

A differential arm 62 is secured to the bevel gears 58, 60. A moving coil 63 is secured to the end of the differential arm 62. The moving coil 63 is partially disposed in a high frequency field induced by an error detector field assembly 65 energized from a high frequency voltage source EAC. A voltage is induced in the moving coil and is fed to the oscillator motor speed controller 40 by flexible leads 66 and conductors 67. The drawing shows the differential arm 6-2 as broken between the moving coil 63 and the error detector diffeerntial so that the moving coil 63 and the field assembly 65 may be shown in perspective to facilitate an understanding of the present invention.

Any movement of the differential arm caused by a differential between the rotational speed of the synchronous motor shaft 54 and the rotational speed of the tubedriven wheel 56 causes the moving coil to travel further into or out of the electromagnetic field. The resultant changeof voltage induced in the moving coil energizes the oscillator motor speed control 40 to either increase or decrease the speed of the oscillator drive motor to place the oscillator drive meachnism back in step with the tube travel.

Thus, the present invention provides a very sensitive and quick-acting tube length control system to accurately relate the operation of the cut-off press to the tube travel. A change in the tube travel causes the moving coil 63 to change the control voltage applied to the oscillator motor speed controller 40. The speed controller 40 then increases or decreases the drive motor speed to automatically change the speed of the oscillator drive mechanism so that it is in step with tube travel. This relation is automatically maintained to assure that all of the tubes will be cut to the same length. A typical motor controller 40 is a rocking contact regulator such as an Allis-Chalmers type VD2. A description of this regulator is found on pages 230, 231 of Control of Electric Motors, by Paisley B. Harwood, published by John Wileyand Sons, Inc., New York, third edition, 1956, Library of Congress catalogue card No. 52-11733.

The length of the tube desired to be cut is selected by adjusting the input shaft speed of the differential selsyn 51. For example, for longer lengths of tube the differential selsyn drive motor is set to rotate the input shaft of the differential selsyn 51 at a faster rotational speed. The differential selsyn increases the frequency of the voltage output of the tachometer generator 45 resulting in an increase in the rotational speed of the output shaft 54 of the synchronous motor 46. This change in speed as detected by the error detector differential of the synchronous control system then decreases the oscillator drive motor speed to place the oscillator drive mechanism back in step with the tube travel. As more tube now travels past the shear member 18 before it makes a cut each tube length is longer. To decrease the lengths of the cut tube, the shaft 52 differential selsyn is driven in a direction so as to subtract from the frequency of the voltage fed to the synchronous motor 46 by the tachometer generator 45. The synchronous control system. again places the oscillator drive mechanism back in step with the tube travel thereby increasing the frequency of the cut as related, for example, to foot of tube travel.

If the differentialbetween the two speeds is beyond the range of the synchronous control system, the differential arm actuates an appropriate one of two range determining limit switches 70, 71. The limit switches 70, 71 are connected to reverse and forward rotation windings 77, 78 respectively, of a rheostat motor 72 which rotates the field in a proper direct-ion rheostat 43 until the speed of the oscillator drive motor is again within the limits of the synchronous control system.

A damping coil 74 and damping capacitor 75 are provided to prevent the synchronous control system from hunting. The coil and capacitor are arrangedin series and are connected to the main supply conductor on each side of the oscillator motor speed controller 40. The damping capacitor and coil do not form a part of the primary feedback loop.

Although the control apparatus of the invention is described in detail above, it is believed to comprise essential-ly a first control circuit producing an output proportional to the speed of operation of the cut-off device, a second control circuit producing an output proportional to actual tube travel and a differential comparator responsive to the first and second control circuits and comparing their outputs in predetermined relation. If either the tube travel or the cutoff device speed should change to alter such predetermined relation the differential comparator adjusts one to place them back in the predetermined relationship. The exact length of the cut pieces is changed by altering at least one of the outputs to temporarily change the predetermined relation.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from. the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A workpiece forming mi-ll comprising:

(a) a forming mechanism for continuously forming a workpiece;

(b) the workpiece forming mechanism including drive means for advancing the workpiece through the mechanism and along a path of travel;

(c) a workpiece cut-off and a cut-off drive mechanism positioned along said path;

(d) the workpiece cut-off drive mechanism including a power means for moving the cut-off drive mecha- 6. nism to permit cutting of the workpiece into lengths as it is moving;

(e) sensing means located at a sensing station along the path of travel between the forming mechanism and the workpiece cut-off, said sensing means being connected to the workpiece and to the cut-off drive mechanism for sensing any change in the relative speed of travel of the workpiece and travel of the cutoff drive mechanism; and,

(f) a speed control connected to the sensing means and one of the mechanisms for changing the speed of the one mechanism each time the sensing means detects a change in relative speed.

2. A control system for use in a continuous mill operation for automatically maintaining the operating speed of a cut-off device in exact step with the travel of a continuously formed workpiece so as to cut the workpiece into uniform preselected lengths, comprising:

(a) a first sensing means responsive to the operating speed of the cut-off device;

(b) a second sensing means responsive to the travel of the workpiece after it has left the last mill operation before cutting;

(c) a differential detector having a first input connected to said first sensing means, a second input connected to said second sensing means, and an output providing a signal in response to a change in a predetermined relation between the operatingspeed of the cut-off device and the travel of the workpiece; and,

(d) control means connected to the differential detector output and responsive to said signal'to adjust the operating speed of said cut-off device to said predetermined relation with the travel of the workpiece;

3. The comibination of claim 2 wherein the cut-off device is a cut-off press including shear and die members.

4. The combination of claim 2 wherein the differential detector includes:

(1) a mechanical differential;

(2) a field assembly establishing an electromagnetic field; and,

(3) a field coil movably carried by said mechanical differential and partially disposed in said electromagnetic field, saidmechanical differential moving said coil relative to the center of said electromagnetic field in response to a change in said predetermined relation, the movement of said coil providing the differential detector output signal.

5. A control system for use in a continuous mill operation for antomatically maintaining the operating speed of a cut-off device in exact step with the travel of a continuously formed workpiece so as to cut the workpiece into uniform preselected lengths, comprising:

(a) a first sensing means responsive to the operating speed of the cutoff device;

(b) a second sensing means responsive to the travel of the workpiece after it has left the last mill operation before cutting;

(c) a differential detector having a first input connected to said first sensing means, a second input connected to said second sensing means, and an output providing a signal in response to a change from a predetermined relation between the operating speed of the cut-off device and the travel of the workpiece;

(d) control means connected to the differential detector output and responsive to said signal to adjust the operating speed of said cut-off device to said predetermined relation with travel of the workpiece; and,

(e) Vernier control means connected to at least one of said sensing means and interjecting a fictitious change from said predetermined relation so that said control means acts to adjust the operating speed of the cut-off device to said predetermined relation and thereby changes the preselected length of the cut pieces of the workpiece.

6. The combination of claim 5 wherein the cut-off device is a cut-off press including shear and die members mounted for movement parallel to the moving workpiece.

7. A synchronous control system for use in a continuous mill operation wherein a tube is continuously moving through a cut-off device comprising:

(a) means responsive to the speed of operation of the cut-off device and producing an output proportional thereto;

(b) means responsive to the tube travel and producing an output proportional thereto; and,

(c) differential comparison means connected to both said responsive means and comparing the speed of operation of the cut-off device to the tube travel and automatically adjusting at least one of said responsive means to maintain both in a predetermined relation so that the cut tubes are of a uniform preselected length.

8. A synchronous control system for use in a continuous mill operation wherein a tube is continuously moving through a cut-off device comprising:

(a) means responsive to the speed of operation of the cut-off device and producing an output proportional thereto;

(b) means responsive to the tube travel and producing an output proportional thereto;

(c) differential comparison means connected to both of said responsive means and comparing the speed of operation of the cut-off device to the tube travel and automatically adjusting at least one to maintain both in a predetermined relation so that the cut tubes are of a uniform preselected length; and,

(d) means to artificially alter at least one of the outputs so that when said differential comparison means operates to maintain the predetermined relation the cut tubes have correspondingly changed to a uniform second preselected length.

9. In a control system for a continuous mill operation wherein a tube is continuously moving through a cut-off device and an oscillator drive mechanism propels the cut-off device back and forth substantially parallel to the tube travel and accelerates the cut-off device to the tube travel speed at the instant the tube is cut, the combination for coordinating said tube travel speed to the operating speed of said oscillator drive mechanism so that a predetermined relation is automatically maintained therebetween to provide cut tubes of a uniform preselected length, said combination comprising:

(a) a tachometer generator having an input shaft operatively connected to an input drive shaft of said oscillator drive mechanism and having an output circuit providing a signal voltage of a frequency proportional to the operating speed of the oscillator drive mechanism;

(b) a synchronous motor having an input circuit connected to said tachometer generator output and an output shaft rotating at the input shaft speed of said tachometer generator;

(c) means sensing the tube travel after the moving tube has left the last mill operation before cutting, said sensing means having an output shaft rotating at a speed proportional to the tube travel;

(d) a differential detector having a first input connected to the output shaft of said synchronous motor and a second input connected to the output shaft of said sensing means, said differential detector comparing the operating speed of the oscillator drive mechanism to the tube travel and providing an out put signal when a predetermined differential occurs therebetween; and,

(e) means controlling said oscillator drive mechanism in response to the differential detector output signal to automatically change the speed thereof to substantially eliminate the differential between the operating speed of said oscillator drive mechanism and the tube travel. 10. 'In a control system for a continuous mill operation wherein a tube is continuously moving through a on -off device and an oscillator drive mechanism propels the cut-off device back and forth substantially parallel to the tube travel and accelerates the cut-off device to the tube travel speed at the instant'the tube is cut,-the combination for coordinating said tube travel to the operating speed of said oscillator drive mechanism so that a predetermined relation is automatically maintained therebetween to provide cut tubes of a'uniform preselected length, said combination comprising:

(a) a tachometer generator having an input shaft operatively connectedto an input drive shaft of said oscillator drive mechanism and having an output circuit providing a signal voltage of'a frequency proportional to the operating speed of the oscillator drive mechanism;

(b) a synchronuousmotor having an input circuit connected to said tachometer generator output and an output shaft rotating at the input shaft speed of said tachometer generator;

(c) means sensing the tube travel after the moving tube has left the last mill operation before cutting, said sensing means having an output shaft rotatmg at a speed proportional to the tube travel,

(d) a differential detector having a first input connected to the output shaft of said synchronous motor and a second input connected to the output shaft of said sensing means, said diiferential detector comparing the operating speed of the oscillator drive mechanism to the tube travel and providing an output signal when a predetermined differential occurs therebetween;

(e) means controlling said oscillator drive mechamsm in response to the differential detector output signal to automatically change the speed thereof to substantially eliminate the differential between the operating speed of said oscillator drive mechanism and the tube travel;

(f) a Vernier selsyn connected to the input circuit of said synchronous motor and the output circuit of the tachometer generator and having an input shaft rotatable to selectively vary the frequency of the tachometer generator signal voltage; and

(g) means rotating the input shaft of the Vernier selsyn in a particular direction and at a preselected speed so that said differential detector provides an output signal in response to the occurrence of said predetermined differential and resulting in a selected uniform change in the length of the cut tubes when controlling means changes the speed of the oscillator drive mechanism to substantially eliminate said predetermined differential.

11. In a control system for a continuous mill operation wherein a tube is continuously moving through a cutoff device and an oscillator drive mechanism propels the cut-off device back and forth substantially parallel to the tube travel and accelerates the cut-off device to the tube travel speed at the instant the tube is cut, the combination for coordinating said tube travel speed to the operating speed of said oscillator drive mechanism so that a predetenmined relation is automatically maintained therebetween to provide cut tubes of a uniform preselected length, said combination comprising:

(a) a first drive assembly for moving the tube through the mill and a second drive assembly for motivating the oscillator drive mechanism;

(b) a first sensing mean-s disposed adjacent the moving tube and operatively associated therewith to provide an output signal proportional to the speed thereof;

Q (o) a second sensing means responsive to the operating speed of said oscillator drive mechanism and providing an output signal proportional thereto; (d) a differential detector connected to said first and second sensing means and comparing the output signal of one to the output signal of the other, said differential detector providing an error signal when a differential exists between said output signals; and, (e) control means responsive to said error signal and controlling at least one of the drive assemblies to automatically change the speed thereof until said error signal indicates that said predetermined relation exists between the tube travel speed and the operating speed of the oscillator drive mechanism. 12. The combination of claim 11 wherein said second sensing means is disposed adjacent said moving tube after it has left the last mill operation before cutting.

13. In a control system for a continuous mill operation wherein a tube is continuously moving through a cut-off device and an oscillator drive mechanism propels the cut-off device back and forth substantially parallel to the tube travel and accelerates the cut-off device to the tube travel speed at the instant the tube is cut, the

combination for coordinating the tube travel to the operating speed of said oscillator drive mechanism so that a preselected relation is automatically maintained therebetiween to provide cut tubes of a uniform exact length, said combination comprising:

(a) a first drive assembly for moving the tube through the mill and a second drive assembly for motivating the oscillator drive mechanism;

(b) a first sensing means disposed adjacent the moving tube and operatively associated therewith to provide an output signal proportional to the per unit speed thereof;

(c) a second sensing means responsive to the operating speed of said oscillator drive mechanism and providing an output signal proportional thereto;

(d) a differential detector connected to said first and second sensing means and comparing the output signal of one to the out-put signal of the other, said differential detector providing an errorsignal when a predetermined differential exists between said output signals;

(e) control means responsive to said error signal and controlling at least one of the drive assemblies to change the speed thereof until said error signal is substantially extinguished such that a predetermined relation is maintained between the tube travel and the'operating speed of the oscillator drive mechanism; and,

(f) at least one of said sensing means including a vernier adjustment means to alter its output signal such that an error signal is provided by said differential detector, and said control means changing the speed of said one of the drive assemblies in response to said error signal so that a second predetermined relation is maintained between the tube travel and the operating speed of the oscillator drive mechanism. t i

14. In a control system for a continuous mill operation wherein a tube is continuously moving through a cutoff device and an oscillator drive mechanism propels the cut-off device back and forth substantially parallel to the tube travel and accelerates the cut-off device to the tube travel speed at the instant the tube is cut, the combination for coordinating said tube travel speed to the operating speed of said oscillator drive mechanism so that a predetermined relation is automatically maintained therebetween to provide cut tubes of a uniform preselected length, said combination comprising:

(a) a first drive assembly for moving the tube through the mill and a second drive assembly for motivating the oscillator drive mechanism;

(is) a first sensing means disposed adjacent the moving 1 bination comprising:

tube and operatively associated therewith to provide an output signal proportional to the speed thereof;

(0) a second sensing means responsive to the operating speed of said oscillator drive mechanism and providing an output signal proportional thereto;

(d) a differential detector connected to said first and second sensing means and comparing the output signal of one to the output signal of the other, said differential detector providing an error signal when a differential exists between said output signals;

(e) control means responsive to said error signal and controlling at least one of the drive assemblies to automatically change the speed thereof until said error signal indicates that said predetermined relation exists betwcn the tube travel speed and the operating speed of the oscillator drive mechanism; and,

(f) vernier means connected to at least one of said sensing means and being adjustable to change the output signal of such sensing means so as to create a differential between said output signals, in which event said control means acts to reduce the differential between the output signals resulting in a selected change in the length of the cut tubes. 7

15. In a control system for a continuous mill operation wherein a tube is continuously moving through a cut-off device and an oscillator drive mechanism propels the cutolfdevice back and forth substantially parallel to thetube travel and accelerates the cut-off device to the tube travel speed at the instant the tube is cut, the combination for coordinating said tube travel to the operating speed of said oscillator drive mechanism so that a predetermined relation is automatically maintained therebet-ween to provide cut tubes of a uniform preselected length, said com- (a) a tachometer generator having an input shaft operatively connected to an input shaft of said oscillator drive mechanism and having an output circuit providing a signal voltage of a frequency proportional to the opera-ting speed of the oscillator drive mechanism;

(b) a synchronous motor having an input circuit connected to said tachometer generator output and an output shaft rotating at the input shaft speed of said tachometer generator;

(0) means sensing the tube travel after the moving tube has left the last mill operation before cutting, said sensing means having an output shaft rotating at a speed proportional to the tube travel;

(d) a differential comparator having a first input connected to the output shaft of said synchronous motor, a second input connected to the output shaft of said sensing means, and a rotating output arm moving in response to a differential between said first and second inputs;

(e;i ird field assembly establishing an electromagnetic (f) a field coil attached to said moving arm and partially disposed in said electromagnetic field;

(g) a speed controller for adjusting the operating speed I of the oscillator drive mechanism; and,

(h) circuit means connecting said speed controller to said field coil whereby a change in the voltage induced in the field coil is indicative of a differential between said first and second inputs and energizes said speed controller to automatically adjust the operating speed of the oscillator drive mechanism to reestablish said predetermined relation between the operating speed of said oscillator drive mechanism and the tube travel.

16. The control system of claim 15 including in combination:

(i) a vernier selsyn connected to the input circuit of said synchronous motor and the output circuit of the tachometer generator and having an input shaft rotatable to selectively vary the frequency of the tachometer signal voltage; and,

i (1 means rotating the input shaft of the Vernier selsyn in a particular direction and at a preselected speed to cause said differential comparator to sense a fictitious change in said predetermined relation between the operating speed of the oscillator drive mechanism and the tube travel in which event the induced voltage in the field coil changes to cause said speed controller to adjust the operating speed of the oscillator drive mechanism to substantially eliminate the differential between the first and second inputs and thereby maintain a second predetermined relation between the operating speed of the oscillator drive mechanism and tube travel, said second predetermined relation providing cut strips of a second uniform preselected length.

17. In a control system for a continuous mill operation wherein a tube is continuously moving through a cut-off device and an oscillator drive mechanism propels the cutoff device back and forth substantially parallel to the tube travel and accelerates the cut-off device to the tube travel speed at the instant the tube is out, the combination for coordinating said tube travel to the operating speed of said oscillator drive mechanism so that a predetermined relation is automatically maintained therebetween to provide cut tubes of a uniform preselected length, said combination comprising:

(a) a variable speed motor driving an input shaft of the oscillator drive mechanism, said motor having an armature circuit and a field winding;

(b) a motor speed controller connected to said armature circuit for selectively varying the speed of said motor and in consequence the speed of said oscillator drive mechanism;

(c) a tachometer generator having an input shaft operatively connected to the input shaft of said oscillat-or drive mechanism and having an output circuit providing a signal voltage of a frequency proportional to the operating speed of the oscillator drive mechanism;

(d) a synchronous motor having an input circuit connected to said tachometer generator output and an output shaft rotating at the input shaft speed of said tachometer generator;

(e) means sensing the tube travel after the moving tube has left the last mill operation before cutting, said sensing means having an output shaft rotating at a speed proportional to the tube travel;

(f) a differential comparator having a first input connected to the output shaft of said synchronous motof, a second input connected to the output shaft of said sensing means, and a rotating output arm moving in response to a differential between said first and second inputs;

(g) a field assembly establishing an electromagnetic field;

(h) a field coil attached to said moving arm and partially disposed in said electromagnetic field;

(i) circuit means connecting said speed controller to said field coil whereby a change in the voltage induced in the field coil is indicative of a differential between said first and second inputs and energizes said controller to automatically adjust the operating speed of the oscillator drive mechanism to reestablish said predetermined relation between the operating speed of said oscillator drive mechanism and the tube travel;

( j) first and second limit switches disposed one on each side of the moving differential arm in a position to be operated by said moving arm when the differential between said first and second inputs is beyond the range of said field coil and the speed controller;

(k) means to vary the voltage applied to said motor field winding and consequently vary the motor speed; and,

(l) circuit means connecting said limit switches to the voltage varying means to adjust the motor speed until it is within the range of the motor speed controller.

13. The control system of claim 17 including in combination:

(m) a Vernier selsyn connected to the input circuit of said synchronous motor and the output circuit of the tachometer generator and having an input shaft rotatable to selectively vary the frequency of the tachometer generator signal voltage; and,

(n) means rotating the input shaft of the Vernier selsyn in a particular direction and at a preselected speed to cause said differential comparator to sense a fictitious change in said predetermined relations between the operating speed of the oscillator drive mechanism and the tube travel in which event the induced voltage in the field coil changes to cause said speed controller to adjust the operating speed of the oscillator drive mechanism to substantially eliminate the differential between the first and second inputs and thereby maintain a second predetermined relation between the operating speed of the oscillator drive mechanism and the tube travel, said second predetermined relation providing cut tubes of a second uniform preselected length.

19. The control system of claim 18 including in combination:

device is a cut-off press including shear and die members mounted for reciprocal movement parallel to the tube travel. I

References (Iited by the Examiner UNITED STATES PATENTS 2/1956 Nelson 318-162 FOREIGN PATENTS 12/1952 Canada.

RICHARD H. EANES, 111., Primary Examiner. 

1. A WORKPIECE FORMING MILL COMPRISING: (A) A FORMING MECHANISM FOR CONTINUOUSLY FORMING A WORKPIECE; (B) THE WORKPIECE FORMING MECHANISM INCLUDING DRIVE MEANS FOR ADVANCING THE WORKPIECE THROUGH THE MECHANISM AND ALONG A PATH OF TRAVEL; (C) A WORKPIECE CUT-OFF AND A CUT-OFF DRIVE MECHANISM POSITIONED ALONG SAID PATH; (D) THE WORKPIECE CUT-OFF DRIVE MECHANISM INCLUDING A POWER MEANS FOR MOVING THE CUT-OFF DRIVE MECHANISM TO PERMIT CUTTING OF THE WORKPIECE INTO LENGTHS AS IT IS MOVING; (E) SENSING MEANS LOCATED AT A SENSING STATION ALONG THE PATH OF TRAVEL BETWEEN THE FORMING MECHANISM AND THE WORKPIECE CUT-OFF, SAID SENSING MEANS BEING CONNECTED TO THE WORKPIECE AND TO THE CUT-OFF DRIVE MECHANISM FOR SENSING ANY CHANGE IN THE RELATIVE SPEED OF TRAVEL OF THE WORKPIECE AND TRVEL OF THE CUT-OFF DRIVE MECHANISM; AND, (F) A SPEED CONTROL CONNECTED TO THE SENSING MEANS AND ONE OF THE MECHANISMS FOR CHANGING THE SPEED OF THE ONE MECHANISM EACH TIME THE SENSING MEANS DETECTS A CHANGE IN RELATIVE SPEED. 